This invention generally relates to optical correlator systems; and more specifically, to multiple channel optical correlator systems.
Optical correlator systems are used to detect the presence of a selected target in a scene or a field of view. In an optical correlator system, a coherent light beam is passed through a view or scene, which may include the selected target, and then transmitted through a matched filter. The matched filter contains a recording of a diffraction pattern unique to the selected target; and if the selected target is present in the submitted view, the matched filter redirects a portion of the beam incident on it into a relatively intense output beam at a selected angle relative to the incident beam, and an inverse transform lens brings this output beam from the matched filter to a focus. However, if the selected target is not present in the submitted view, any output beam of the matched filter at this selected angle is relatively weak and diffused. A light sensitive detector is located in the focal plane of the inverse transform lens; and when light of a sufficient intensity is focused on that detector, an output signal is produced. This output signal is used to trigger some type of device, which, depending on the apparatus in which the target recognition system is used, might be a simple alarm or a complex robotic guidance system, for example.
The capacity of an optical correlator system can be significantly increased by providing the system with a matched filter having a multitude of recorded diffraction patterns. This multi-channel memory can be addressed by a multiple focus holographic lens, or MHL, which can replicate and Fourier transform an input image. Each of the diffraction patterns stored in the memory may be unique to a respective view of one target, or these diffraction patterns may represent plural targets, and a correlator system having a multitude of such diffraction patterns may be used to detect a target in a scene independent of the orientation of the target in that scene, or to detect plural targets in one scene.
In order to improve the response time and the storage capacity of a correlator system having a multitude of recorded diffraction patterns, commonly the modulated signal beam is replicated manifold, and each replica beam is focused on a respective one of the recorded diffraction patterns. Various prior art techniques are known to replicate the modulated signal beam, and, for example, a multiple beam generating holographic element may be used for this purpose. While these prior art arrangements are normally satisfactory, it is nonetheless believed that their efficiency can be improved. In particular, while these multichannel correlator systems have increased capacity relative to conventional single channel systems, it is nonetheless believed that the capacity of multichannel systems can be further increased without significantly increasing either the size or the cost of the systems.